For example, create task and set tags
$data = array('jsonrpc'=>'2.0',
'method'=>'createTask',
'id'=>'1',
'params'=> array ('owner_id'=> 0,
'creator_id'=> 3,
'date_due'=> '',
'description'=> 'task_desk',
'category_id'=> 0,
'score'=> 0,
'title'=> 'task_title',
'project_id'=> 1,
'column_id'=> 0,
//add tags
'tags'=> array('tag1name'=> 'tag1content', 'tag2name'=> 'tag2content)
));
$curl = curl_init();
curl_setopt($curl, CURLOPT_URL,'KANBOARD_URL/jsonrpc.php');
curl_setopt($curl, CURLOPT_POST, 1);
curl_setopt($curl, CURLOPT_USERPWD, 'jsonrpc:API_KEY');
curl_setopt($curl, CURLOPT_POSTFIELDS, json_encode($data));
$result = curl_exec ($curl);
curl_close ($curl);